I have finally managed to create a workable
Windows program to allow matching published
(or measured) curves. Once that is done you
will have a nice Spice model for accurately
designing circuits. And you can print have
the program print out the set of curves in
presentation quality.

The program uses the Koren parameters. You
adjust those to make the program-generated
curves match (by overlay) the published curves.
At that point the Spice model is available.

The file at that location is an installer which
installs the program "TubeCurves". To use that
program is not all that obvious so here are some
suggestions.

It would be a very good idea to print out this
stuff so you can go through it step by step until
you "get the hang of it" and then you can go off
on your own.

After the program is installed, start
"TubeCurves.exe" and you will see the opening
screen. (I had fun with the graphic!)

Click on "Start"
See the "Initialize" screen
Click on "Get old design"
For this trial, click on "12AU7design"
Then click on "Open"
Click on "Get graphic"
For this trial, click on "1-12AU7.jpg"
Then click on "Open"
If you have been living a good life then the
computed plot will overlay on the called-up
graphic. If not, use the buttons in the upper-right
corner to make the outside of the computed plot
agree with the graphic.
Before leaving this page, remember the maximum
volts and amps.
Click on "Continue"
You may now have fun with what I have been
calling the Koren Variables. You can step them
with the buttons or enter tuff into the textboxes.
If you go the latter route, click on the "Refresh"
button to accept those entered values.
Option: if everything matches satifactorily, you
may click on "Save" to store that design to the
hard drive.
To onward, click on "Examine"
This allows you to rescale things so that the fullscale
values are more to your liking. I suggest, for example,
using a fullscale voltage value of 400 volts, step 50.
And perhaps 20 milliamperes step 5 mills. By the
way, the internal parser accepts "m" for millli. Etc.
The full Spice set of prefixes. (Except "M" is for
mega-)

You should be able to match the published graphic.

Now - here is a real slick thing: you can extract from
the plot the value of mu and also of Gm at a given
operating point. This is quite hard to put into print
but I'll try.

At a given operating point, put the curser on a blue
line immediately above or below your operating
point and left-click. Then go ONE BLUE LINE
VERTICALLY and right-click. The value of Gm
will show in the upper-left corner.

Similarly, you can extract the value of mu at a given
point by left-clicking at a given current, on a blue
line, and then moving to the same current, left or
right to the nest blue line and right-clicking. The
value of mu will show in the upper-left corner.

This program will write nice circuit files as well as
a nice test circuit for LTspice. Since you fellows
are well-versed on those things I won't pursue that
except to suggest you try it.

This program is fine for the usual audio fellow who
wants to generate a Spice model so he can accurately
design amplifiers. It also allows generating nicely-
printed families of curves for a given tube.

It does not do grid current. I would hope that based
on this effort it could be expanded to do that and
also do tetrodes and pentodes, hopefully with screen
current as well. However, I don't have the math or
tube smarts to do that on my own. Give me the
equations and I can probably move forward on that
front.

I contacted Jim and discovered that the link above is broken because he updated the software's revision number. Here's the current link. If it breaks again sometime in the future, just try higher numbers in the filename.